Thoracophagus is a fetal abnormality consisting of conjoint twins united in or near the thoracic region. Conjoined twinning occurs in 1 in 100 sets of monozygotic twins, 1 in 50,000 gestations or 1 in 250,000 live births. There is a greater incidence (70%) of female conjoined twin but the reason is unknown. At about 2nd week in the normal twinning process, the inner cell mass splits into two separate and nearly equal halves each usually producing a single individual. Conjoined twins will be of the same sex. Conjoint twins may be joined at any of these following sites: Chest, abdomen, base of spine, length of spine, pelvis, trunk, head, and head and chest. In rare cases, twins may be conjoined with one twin smaller and less fully formed than the other (asymmetric conjoined twins). In extremely rare cases, one twin may be found partially developed within the other twin (fetus in fetu). Conjointment is seen as a medical condition that requires treatment, and the indicated treatment is invasive surgery to complete the process of splitting that was halted in the womb. Surgical separation of nearly complete conjoined twins may be successful when organs essential for life are not shared. It must be remembered that monozygotic twins are at increased risk to be discordant for structural malformations, most likely because the process of twinning is a teratogenic event which disturbs the timing of normal developmental processes. As a result, conjoined twins may have a discordant structural anomaly that further complicates decisions about whether or not to continue the pregnancy.
Conjoint twinning is a condition in which the twins are physically joined at birth, sometimes sharing organs, and in some cases separable by surgery (depending on the degree of fusion)
Monozygotic twins are identical twins. They result from the fertilization of a single egg that splits in two. Identical twins share all of their genes and are always of the same sex.
Gestation is the process or period of development inside the womb between conception and birth.
Live birth is a birth at which the child is born alive.
Teratogenesis is the process by which congenital malformations are produced in an embryo or fetus. It is a prenatal toxicity characterized by structural or functional defects in the developing embryo or fetus. It also includes intrauterine growth retardation, death of the embryo or fetus, and transplacental carcinogenesis